There are known gas masks and protective breathing devices used to insure safe breathing in situations where harmful or deadly air is generated, such as in fire emergencies, chemical or biological warfare, or industrial chemical gas hazards. As referred to herein, the term "toxic air" will be used to refer to gases generated by fire, solid particles, smoke particulate matter, chemical warfare agents, including nerve agents, blood agents, choking agents and blister agents, biological warfare agents such as anthrax, botulinium, and hazardous industrial chemical gases, such as ammonia, chlorine, carbon tet, etc.
While there are well-developed protective breathing devices used by firefighting personnel entering the scene of a fire to rescue fire victims, the general public has not used them.
In recent years, there have become available lightweight, portable protective breathing masks for use by civilians, to reduce smoke inhalation mortality rates. These devices are designed with the recognition that in fire emergencies, immediately upon the outbreak of a fire, every second becomes precious in the preservation of life. By the time firefighters arrive at the scene of the fire and locate the victims for rescue procedures, many victims have been overcome with toxic air and may be unconscious and unable to aid the rescue efforts. Untold numbers of fire victims perish not by contact with flames, but through an inability to breathe just long enough to safely exit burning buildings, or be located and rescued by firefighters. A prime example of an institution requiring these devices is a tourist hotel, where many tragic fire fatalities of the past may have been avoided were protective breathing masks instantly available.
Examples of the protective breathing masks available in the market include the mask described in U.S. Pat. No. 4,870,959 to Reisman, owned by the owners of the present invention. The patent discloses a protective breathing mask made of fire-resistant, stretchable elastomeric material shaped as a hood with an access opening through which the head is placed for wearing the mask over the head and enclosing it such that a substantially airtight closure is provided at the neck. A portion of the mask is provided with a transparent visor for the eyes, and the hood has filter materials sealed thereto at a mouth location, with the filter comprising a plurality of fire-resistant flexible layers, at least one of which having embedded therein activated charcoal.
Other examples of protective breathing masks include that described in U.S. Pat. No. 5,392,465 to Shou, which describes a mask made of fireproof cloth impregnated with a smoke preventing chemical substance, and having a transparent visor. U.S. Pat. No. 5,214,803 to Schichman describes a smoke hood which can be secured substantially airtight about the user's neck and filled with ambient air to enable breathing of the air within the hood, for a predetermined time, free of external air.
U.S. Pat. No. 5,146,636 to De La Pena discloses a heat and smoke protective hood comprising a bag-like head covering of a heat-resistant, substantially gas-impermeable sheet material adapted to fit loosely over the head, with a filter provided in an aperture of the hood covering, and a stretchable annular neck portion attached to an open end of the head covering for sealing around the neck.
U.S. Pat. No. 4,935,966 Hosouchi et al discloses a smokeproof foldable bag having an opening which, when unfolded, can be used to receive a person's head therein, to prevent smoke inhalation during a fire. A fire and smoke protective hood is disclosed by U.S. Pat. No. 5,113,527 to Robertson-McKenzie, and is made from a high temperature-resistant plastics material coated on its exterior with a layer of titanium to reflect heat.
Among the goals in design of protective breathing masks as aforementioned is the desire to achieve easy breathing. In achieving this goal, two of the design constraints faced are related to the type of filter used and the interior mask volume, which determines the amount of "dead space" once the user dons the mask. Those masks which have a stretchable hood, such as the Reisman patent, minimize the "dead space" by pressing the filter close up against the mouth, and achieve easy breathing by use of a thin filter which provides low resistance to exhaled air. These features tend to reduce psychological pressure on the user, since they assist in minimizing the buildup of heat, vapor and CO2 gas.
A drawback in the existing designs which minimize the "dead space" is that by pressing the filter against the mouth and nose, the filter surface area is not effectively utilized and uneven airflow distribution is provided, reducing the useful filter protection time. An inverse relationship exists between increased protection time and easy breathing, since increasing the filter materials increases resistance. Alternatively, by increasing the space between the mouth, nose and the filter, air distribution is more uniform, and thus the filter utilization is improved. However, the "dead space" increases, exacerbating the psychological effects, due to heat, vapor and CO2 gas buildup.
It would therefore be desirable to provide a protective breathing device which, in addition to being convenient, affordable and instantly available to civilians in toxic air emergencies, achieves easy breathing and increased protection time.